The present invention relates to an active anti-vibration device used in a semiconductor exposure apparatus or liquid crystal substrate manufacturing apparatus for transferring and printing a circuit pattern on a reticle onto a semiconductor wafer, an electron microscope, or the like and, more particularly, to an anti-vibration device using a displacement generation element represented by a piezoelectric element or like, i.e., a displacement generation actuator active vibration isolation device comprising a versatile feedback process encompassing the prior art.
Also, the present invention relates to a hybrid active vibration isolation apparatus using an anti-vibration unit which integrates a displacement generation actuator (e.g., a piezoelectric element) and a force actuator (e.g., an electromagnetic motor).
In an electron microscope using an electron beam or a semiconductor manufacturing apparatus represented by a stepper, scanner, or the like, an X-Y stage is placed on an anti-vibration unit. The anti-vibration unit has a function of damping vibration by vibration absorbing means such as an air spring, coil spring, anti-vibration rubber, and the like. However, a passive anti-vibration unit having such vibration absorbing means can damp vibration that propagates from a floor to some extent, but cannot effectively damp vibration produced by the X-Y stage itself. That is, the counter force produced by high-speed movement of the X-Y stage itself vibrates the anti-vibration unit, and this vibration considerably impairs alignment settling performance of the X-Y stage.
Furthermore, the passive anti-vibration unit suffers a tradeoff between isolation of vibration (vibration isolation) that propagates from the floor, and suppression of vibration (vibration damping) produced upon generation of high-speed movement of the X-Y stage itself. To solve such problems, an active anti-vibration unit has been used more often in recent years. The active anti-vibration unit can eliminate the tradeoff between vibration isolation and vibration damping within the range of an adjustable mechanism, and can get performance that cannot be achieved by a passive anti-vibration unit by positively applying feedforward control.
However, in order to further suppress propagation of vibration to apparatuses that cannot tolerate vibration represented by a semiconductor manufacturing apparatus, vibration isolation is required for a still lower frequency range. For this purpose, attempts have been made to use an active vibration isolation device using a piezoelectric element, which can accurately control infinitesimal displacement, in vibration isolation of the entire semiconductor manufacturing apparatus. However, an anti-vibration device using an air spring or electromagnetic motor has been developed remarkably and has reached a practical level, but an active vibration isolation device using a piezoelectric element as an actuator stays at the level of laboratory study. The arrangement of its controller has not been examined extensively, and the performance of the piezoelectric element cannot be fully utilized.
The active vibration isolation device using a piezoelectric element that represents a displacement generation actuator includes three different types. The first type (type A) drives a piezoelectric element 1 on the basis of a signal output from a vibration detection means 9b on an intermediate plate 5, as shown in FIG. 7A. The second type (type B) drives a piezoelectric element 1 on the basis of outputs from vibration detection means 9b and 9a provided on an intermediate plate 5 and an object from which vibration is to be removed (to be referred as vibration damping subject) 4, as shown in FIG. 7B. The third type (type C) drives a force actuator 6 provided between an intermediate plate 5 and vibration damping subject 4 together with a piezoelectric element 1 on the basis of outputs from vibration detection means 9a, 9b, and 9c mounted on the vibration damping subject 4, the intermediate plate 5, and a floor 10, as shown in FIG. 7C. Higher performance characteristics are assured in the order of FIGS. 7A, 7B, and 7C.
Skipping an analysis for the arrangement shown in FIG. 7A, the feedback arrangement in FIG. 7B will be explained first. FIG. 8 shows a structure of an anti-vibration unit in which a piezoelectric element is built in as an actuator. Referring to FIG. 8, reference numeral 1 denotes a piezoelectric element; 2, a leaf spring; 3, laminated rubber; 4, a stepper, for example, as a vibration damping subject; and 5, an intermediate plate. FIGS. 9A and 9B respectively show a dynamics model of this structure and feedback control executed for this structure. This structure is disclosed in Japanese Patent Laid-Open No. 8-54039 (stiff actuator active vibration isolation system: U.S. Pat. No. 5,660,255). Using reference symbols in FIGS. 9A and 9B, equations of motion are given by:
MPs2x=(Ki+Cis)(vxe2x88x92x)+fpxe2x80x83xe2x80x83(1)
MSs2v=KS(zxe2x88x92v)+(Ki+Cis)(xxe2x88x92v)xe2x80x83xe2x80x83(2)
where MP is the mass of the vibration damping subject 4, Ki is the spring constant of the laminated rubber 3, Ci is the viscous damping coefficient of mainly the laminated rubber 3 between the vibration damping subject 4 and intermediate plate 5, MS is the mass of the intermediate plate 5, KS is the spring constant of the piezoelectric element 1, x is the displacement of the vibration damping subject 4, v is the displacement of the intermediate plate 5, u is the displacement of floor vibration, z is the displacement of the piezoelectric element 1, and fp is disturbance acting on the vibration damping subject 4.
Analysis will be again given first considering the technical contents disclosed in Japanese Patent Laid-Open No. 8-54039 (stiff actuator active vibration isolation system: U.S. Pat. No. 5,660,255). FIG. 9B is a block diagram that explains the feedback arrangement of the active vibration insulation device which uses the piezoelectric element as an actuator, as given by equations (1) and (2). As illustrated in FIG. 9B, there are two feedback loops. Using symbols in FIG. 9B, a feedback equation is given by:
z=uxe2x88x92Cdvxe2x88x92CVsxxe2x80x83xe2x80x83(3)
where Cd is the feedback gain of the absolute displacement, and Cv is the feedback gain of the absolute velocity. From equations (1) to (3), the relationship among the displacement x of the vibration damping subject, the displacement u of floor vibration, and the disturbance fp is given by:                     x        =                                                                              (                                                                                    C                        i                                            ⁢                      s                                        +                                          K                      i                                                        )                                ⁢                                  K                  s                                                            D                ⁡                                  (                  s                  )                                                      ·            u                    +                                                                                          M                    s                                    ⁢                                      s                    2                                                  +                                                      C                    i                                    ⁢                  s                                +                                  K                  i                                +                                                      K                    s                                    ⁡                                      (                                          1                      +                                              C                        d                                                              )                                                                              D                ⁡                                  (                  s                  )                                                      ·                          f              p                                                          (        4        )            xe2x80x83D(s)=MPMss4+(Mp+MS)Cis3+[MP{Ki+Ks(1+Cd)}+MSKi+CiKsCV]s2{CiKS(1+Cd)+KiKSCV}s+KiKS(1+Cd)xe2x80x83xe2x80x83(5)
From the above equations, the transmissibility from the displacement u of floor vibration to the displacement x of the vibration damping subject with the mass MP is defined by the first term of the right-hand side of equation (4). If sxe2x86x920, the transmissibility in the DC range is given by:                               x          u                =                              1                          1              +                              C                d                                               less than                       0            ⁢                          xe2x80x83                        [            dB            ]                                              (        6        )            
That is the transmissibility in the DC range can be set below 0 [dB] by adjusting the gain Cd. This is a critical difference from an anti-vibration device using an air spring or electromagnetic actuator. Normally, in an active anti-vibration device using an air spring as an actuator, damping is given by a vibration control loop based on detection of acceleration (absolute acceleration), and the designated posture is maintained by a position control loop based on the relative displacement between a floor and anti-vibration base. Since the relative displacement is fed back, the transmissibility in the low-frequency range is 0 [dB] but never falls below this value. Equation (6) can be implemented only because the absolute displacement is fed back at the gain Cd. In other words, a skyhook spring is implemented by feeding back the absolute displacement.
The skyhook spring can also be implemented in principle by, e.g., an anti-vibration device using an air spring as an actuator. That is, characteristics from the input to a servo valve for driving the air spring until the pressure at which the air spring is generated can be roughly considered as integral characteristics. Taking into account such characteristics, the acceleration of an anti-vibration base supported by the air spring is detected, and is negatively fed back to the input to the servo valve via integral compensation. With such feedback, the skyhook spring can also be implemented by an anti-vibration base using an air spring as an actuator in principle. However, in fact, there has been no report on implementation and actual operation of a skyhook spring in an anti-vibration device using a force generation actuator such as an air spring, electromagnetic motor represented by a linear motor, or the like. Displacement can be precisely controlled by using a piezoelectric element or the like that represents a displacement generation actuator, and hence, stiffness can also be precisely controlled. That is, it is difficult to implement a skyhook spring using a force generation actuator in practice.
The response from the disturbance fp to x is defined by the second term of the right-hand side of equation (4), and if sxe2x86x920, the response in the DC range is given by:                               x                      f            p                          =                              1                          K              i                                +                      1                                          K                s                            ⁡                              (                                  1                  +                                      C                    d                                                  )                                                                        (        7        )            
The above equation describes the compliance of a series spring system. The first term indicates the compliance of the hard rubber 3 inserted between the intermediate plate 5 and vibration damping subject 4, and the second term indicates the compliance of a spring between the piezoelectric element 1 and intermediate plate 5 and a spring produced by feedback. As can be seen from the second term, a spring KS between the piezoelectric element 1 and intermediate plate 5 and a spring KSCd produced by the absolute displacement feedback are connected in parallel with each other. By increasing the gain Cd, the compliance given by equation (7) lowers and vibration damping characteristics improve. However, the magnitude of the compliance cannot become smaller than the first term.
From the above description, the effect of Cd can be explicitly explained on the basis of the two static relations, i.e., equations (6) and (7).
The effect of CV will be explained below. The function of CV is obvious if one examines coefficients associated with the s2 and s terms of characteristic equation (5) or refers to the block diagram in FIG. 9B. The viscous damping coefficient having a magnitude KSCV is produced by feeding back the gain CV. That is, damping is given to a mechanism to stabilize it.
With the above analysis, the conventional control technique disclosed by Japanese Patent Laid-Open No. 8-54039 (stiff actuator active vibration isolation system: U.S. Pat. No. 5,660,255) is understood. That is, damping is given to the mechanism by feeding back the absolute velocity of the gain CV, and stiffness is electrically increased by feeding back the absolute displacement of the gain Cd, thereby making the transmissibility in the low-frequency range fall below 0 [dB].
Meanwhile, in the feedback arrangement shown in FIG. 7C, since the numbers of sensors and actuators are larger than those in FIG. 7B, the control characteristics can be improved. However, the feedback arrangement for such hybrid active vibration isolation device has not been fully explored yet.
An active vibration isolation device that assembles a piezoelectric element or the like as a representative displacement generation actuator has been extensively studied to be practically applied to semiconductor manufacturing apparatuses. However, a control technique that can fully exploit the feature of the piezoelectric element has not been established yet as compared to an active anti-vibration device using an air spring or electromagnetic actuator.
Especially, the control technique for a hybrid active vibration isolation device which uses both a displacement generation actuator represented by a piezoelectric element, and a force generation actuator represented by an electromagnetic motor leaves much to be desired, and the arrangement itself of a hybrid active vibration isolation device that can be applied to a semiconductor exposure apparatus has not been established yet.
The reason why a control technique that can sufficiently exploit the feature of the piezoelectric element has not been established as compared to the active anti-vibration device using an air spring or electromagnetic motor is as follows.
(1) Conventionally, in order to further improve vibration isolation characteristics of a vibration damping subject with unknown dynamics, an anti-vibration unit in an active vibration isolation device is additionally inserted, and no geometric information that pertains to the layout is obtained in advance of such information cannot be obtained.
(2) The anti-vibration unit itself constructs an interconnected dynamics system. That is, one anti-vibration unit has vibration detection means respectively for the floor, intermediate plate, and vibration damping subject. When a plurality of such anti-vibration units are used, how to get the dynamics of the individual intermediate plates to cooperate is indeterminate. However, from the standpoint that the dynamics of the vibration damping subject are thoroughly known, independent operations of a plurality of anti-vibration units mean idle operation; also, maximum anti-vibration characteristics cannot be obtained. That is, effective vibration isolation is hardly achieved. On the other hand, from the standpoint of positively introducing an anti-vibration unit, since information that pertains to the geometric layout of a plurality of anti-vibration units and the dynamics of the vibration damping subject are known, problem (1) above remains unsolved.
The present invention has been made in consideration of the above situation, and has as its object to provide an active anti-vibration device and its control method, which can implement effective vibration isolation using both a force generation actuator and a displacement generation actuator.
It is another object of the present invention to allow the force generation actuator to effectively exhibit anti-vibration performance.
It is still another object of the present invention to allow an anti-vibration device using a displacement element such as a piezoelectric element or the like as an actuator to effectively exhibit an anti-vibration function.
A hybrid active vibration isolation device according to one aspect of the present invention comprises an intermediate plate inserted between a vibration damping subject and a setting surface on which the vibration damping subject is set, an elastic body and force generation actuator inserted in parallel with each other between the vibration damping subject and intermediate plate, a displacement generation actuator inserted between the intermediate plate and setting surface, first, second, and third vibration detection means for respectively detecting vibrations of the vibration damping subject, intermediate plate, and setting surface, and feedback control means for driving the force generation actuator by a sum signal of signals obtained by performing predetermined compensation for outputs from the first and third vibration detection means, and driving the displacement generation actuator by a signal obtained by performing predetermined compensation for an output from the second vibration detection means.
A hybrid active vibration isolation device according to another aspect of the present invention comprises a plurality of anti-vibration units according to the aforementioned hybrid active vibration isolation device, and comprises first motion mode extraction arithmetic means for calculating a motion mode of the vibration damping subject on the basis of the outputs from the first vibration detection means of the respective anti-vibration units, a first PID compensator for performing predetermined compensation for signals that represent rigid body and elastic motions and output from the first motion mode extraction arithmetic means, first motion mode distribution arithmetic means for receiving the output from the first PID compensator, a driver for driving the force generation actuators of the respective anti-vibration units by receiving the output from the first motion mode distribution arithmetic means as an input, second motion mode extraction arithmetic means for cooperating the intermediate plates of the respective anti-vibration units on the basis of the outputs from the second vibration detection means of the respective anti-vibration units, a second PID compensator for performing predetermined compensation for the output from the second motion mode extraction arithmetic means, second motion mode distribution arithmetic means for receiving the output from the second PID compensator as an input, a high-voltage amplifier for making the displacement generation actuators of the respective anti-vibration units generate displacement on the basis of the output signal from the second motion mode distribution arithmetic means, and a third PID compensator for performing predetermined compensation for the outputs from the third vibration detection means of the respective anti-vibration units, which are added to the inputs to the driver.
According to this aspect, control that can fully exploit the feature of the force generation actuator can be made, and vibration isolation/vibration damping that can be applied to a semiconductor exposure apparatus or the like can be implemented. Also, the respective anti-vibration units can efficiently cooperate, thus achieving effective vibration isolation.
In order to achieve the above objects, according to still another aspect of the present invention, a vibration isolation device which sets a vibration damping subject, that is coupled to an intermediate plate via an elastic body, at a setting position via the intermediate plate and a displacement generation actuator, and drives the intermediate plate by the displacement generation actuator, detects vibration of the individual building components in a system from the vibration damping subject to the setting position, performs specific conversion for a vibration detection signal, and drives the displacement generation actuator by the converted signal.
According to one aspect, a displacement generation actuator active vibration isolation device of the present invention detects the absolute velocities of an intermediate plate and vibration damping subject, inputs the detection signals of these absolute velocities to corresponding PID compensators, and drives a displacement generation actuator on the basis of a sum signal of the outputs from the PID compensators.
According to another aspect, the apparatus detects the absolute accelerations of the intermediate plate and vibration damping subject, inputs the detection signals of these absolute accelerations to corresponding PII2 compensator, and drives the displacement generation actuator on the basis of a sum signal of the outputs from the PII2 compensators.
According to still another aspect, load sensors are provided between the vibration damping subject and an elastic body, and between the intermediate plate and displacement generation actuator, and the displacement generation actuator is driven on the basis of the, outputs from the load sensors. The outputs from the load sensors are supplied to corresponding PII2 compensators like in the above aspect, and the displacement generation actuator can be driven based on a sum signal of the outputs from the PII2 compensators.
According to still another aspect, the absolute acceleration of floor vibration at the setting position is detected, the detection signal of this absolute acceleration is input to a double integrator or double pseudo integrator, and the displacement generation actuator can be driven based on the output from the integrator.
According to still another aspect, the absolute velocity of floor vibration at the setting position is detected, the detection signal of this absolute velocity is input to an integrator or pseudo integrator, and the displacement generation actuator can be driven based on the output from the integrator.
According to still another aspect, smart units each using a displacement generation actuator are attached to a post and brace as mechanism members below a clean room where the vibration damping subject is set. The smart unit has a function of applying a force to the post or brace using a piezoelectric element or the like as an actuator and making it expand/contract or bend.
The above-mentioned vibration damping subject is a semiconductor manufacturing apparatus represented by a stepper, scanner, or the like. As the displacement generation actuator, a piezoelectric element, electrostrictive element, or the like is suitably used.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.